This is the generic class for pulse or digital communication
systems using electrical or electromagnetic signals. Such
communication includes transmitting an intelligence bearing signal
from one point to another in the form of discrete variations in
some parameter of the electrical or electromagnetic signal.

SECTION II - LINES WITH OTHER CLASSES AND WITHIN THIS CLASS

Telegraph and printing telegraph systems which include transmission
or reception of a carrier are classified in Class 375 except for
those systems specifically provided elsewhere, such as
a spark gap and a coherer. See References to Other Classes, below.

A carrier which is modulated by a continuously variable (analog) signal
is classified elsewhere (See References to Other Classes, below).
A device which is convertible from analog to pulse or digital may
have a time related parameter (e.g., pulse
width, or repetition rate) continuously variable
and be classified herein.

Light Wave Communication is classified elsewhere (See
References to Other Classes, below), regardless
of the type of modulation.

Duplexing or Multiplexing systems which utilize pulse or digital
information signals are classified elsewhere (See References
to Other Classes, below).

Code converters which may be utilized in a pulse or digital
communication system, are classified elsewhere (See
References to Other Classes, below).

Addressing of a particular pulse receiver is classified elsewhere (See
References to Other Classes, below).

The combination of the subject matter of this class (375) and
another art environment is generally classified with the other art
environment where that environment is significant by virtue of the
claimed relationship. For example: Error checking
systems; Electroacoustic geophysical systems; Dynamic
Magnetic Information Storage or Retrieval; Radar systems; Directive
systems; Telemetering systems; Television. See
References to Other Classes, below.

Remote control of a transmitter and/or receiver is
classified herein; however, the remote control
of a device external to a communication system is classified elsewhere. Remote
control of an external device by light wave communications is classified
elsewhere. See References to Other Classes, below.

Electrical circuits or devices which may use pulse or digital
handling techniques, but are not unique to communications, are
classified in the appropriate classes. For example: Pulse
characteristic discriminating, comparing or selecting. Pulse
responsive selective systems; Pulse demodulation, per
se; Pulse modulation converters to FM; Pulse modulation, per
se; Pulse generating oscillator; pulse counting
circuits and systems; Pulse counters and dividers; Pulse
shaping or converting; Digital comparator systems; Data
conversion. See References to Other Classes, below.

Digital television bandwidth reduction or expansion system
is classified in Class 375, subclasses 240.01-240.29; analog
television bandwidth reduction or expansion is classified with the
television art. See References to Other Classes, below.

Electricity: Measuring and Testing,
subclasses 76.12+ for analysis of complex waves; subclasses
76.39+ for measuring the repetition rate of pulses; and
subclasses 76.77+ for the phase comparison of
pulse voltages.

Communications, Electrical:
Acoustic Wave Systems and Devices, appropriate subclass for the communication of information
in the form of traveling stresses in an elastic medium;
subclasses 14+ for electroacoustic geophysical systems.

Telecommunications, for a carrier which is modulated by a continuously
variable (analog) signal. however, simultaneous
transmission of independent analog and pulse or digital information
bearing signals is classified elsewhere.

This subclass is indented under the class definition. Subject matter utilizing a data modulated signal which has
its energy spread over a transmitted bandwidth which is much greater
than the bandwidth or rate of information being sent.

(1)Note. Four general types of modulation that are
in the spread spectrum variety:

(a) Modulation of a carrier by a data modulation signal whose
bit rate is much higher than the maximum possible repetition rate
of the pulses or discrete steps. Such systems are called "direct sequence" modulated
systems.

(b) Carrier frequency shifting in discrete increments in a pattern
dictated by a code sequence. These are called "frequency
hoppers." The transmitter jumps from frequency to frequency
within some predetermined set; the order of frequency usage
is determined by a code sequence.

(c) Pulse-FM or "chirp" modulation, in which
a carrier is swept over a wideband during a given pulse interval.

(d) Ultra-wideband or ultra-short pulse modulation, in
which information is transmitted using extremely short-duration
signals.

(3)Note. Closely akin to the frequency hoppers are
"time hopping" and "time-frequency hopping" systems,
whose chief distinguishing feature is that their time of transmission (usually
of low duty cycle and short duration) is governed by a
code sequence. In time-frequency hoppers it follows
that the code sequence determines both the transmitted frequency
and the time of transmission.

Electrical Computers: Arithmetic Processing
and Calculating,
subclasses 250 through 256,314, and 422-426, respectively, for
random number or sequence generation, matched filtering
and correlators implemented in the types of systems found in this class.
Chirp signal processing techniques per se are classified in subclasses
400-410.

This subclass is indented under subclass 130. Subject matter including a system in which the wide band
signal is generated by jumping from one frequency to another over
multiple number of frequency choices.

This subclass is indented under subclass 130. Subject matter including a system wherein waveforms are
transmitted at times which are selected from among a plurality of
time slots, with the selection of time slot being pseudo-random, if
desired.

This subclass is indented under subclass 130. Subject matter including a signal format in which a pulsed
carrier is transmitted and is varied continuously in frequency in
a known way during the transmission of a given pulse.

This subclass is indented under subclass 141. Subject matter in which transmitted signals are recovered
using a structure or method that compares a transmitted spreading
code sequence with a local spreading code sequence, generally
by multiplicative means.

This subclass is indented under subclass 141. Subject matter in which transmitted signals are recovered
using a structure or method that is designed to pass only the specific
transmitted signal (i.e., spreading
code), that is matched to the spreading code used
to transmit the signal.

This subclass is indented under subclass 141. Subject matter in which transmitted signals are recovered
using a structure or method that either recovers multiple simultaneously-transmitted
signals or recovers a transmitted signal and rejects spurious signals.

This subclass is indented under subclass 141. Subject matter in which methods, involving the transmission
of specific types of patterns or waveforms, are used to
insure that proper spreading sequence timing is used at the receiver.

This subclass is indented under subclass 147. Subject matter in which transmitted signals are recovered
using a structure or method that either recovers multiple simultaneously-transmitted
signals or recovers a transmitted signal and rejects spurious signals.

This subclass is indented under subclass 147. Subject matter in which transmitted signals are recovered
using a structure or method that compares a transmitted spreading
code sequence with a local spreading code sequence, generally
by multiplicative means.

This subclass is indented under subclass 147. Subject matter in which transmitted signals are recovered
using a structure or method that is designed to pass only the specific
transmitted signal (i.e., spreading
code), that is, it is a matched to the
spreading code used to transmit the signal.

This subclass is indented under subclass 211. Subject matter including conversion (e.g., multilevel
to binary or parallel-serial-parallel) or where
signal pulses are regenerated as regards shape and instant of occurrence.

This subclass is indented under subclass 214. Subject matter having a closed-loop electronic servomechanism
the output of which locks onto and tracks a received clock signal
to provide the frequency and phase aligned receiver clock.

This subclass is indented under the class definition. Subject matter wherein the transmission system, transmitter, or
receiver may be altered to alternately send either digital or analog information.

(1)Note. Systems or elements that simultaneously convey
analog and digital information are not in this class but in Class 370, Multiplex. Systems
wherein the digital data is the address signal for the analog message
are not here but in Class 340, subclasses 7.2-7.63.

This subclass is indented under subclass 216. Subject matter including a means to automatically quiet
the receiver by reducing its gain in response to a specified characteristic
of the input digital signal.

This subclass is indented under the class definition. Subject matter in which a transmitter and a receiver are
at the same location and transmit and receive over the same medium
to-and-from the same remote station.

(1)Note. The simultaneous operation of a transmitter
and receiver is a duplex operation and is classified in Class 370, Multiplex
Communications, subclasses 276+.

(2)Note. This and indented subclasses accept nominal
recitation of a digital data processing system or function in combination
with transceivers and data sets. Significant digital data
pre- and postprocessing in combination with transceivers
are classified elsewhere.

Electrical Computers and Digital Data Processing
Systems: Input/Output,
subclasses 1+ for transferring data from one or more peripherals
to one or more computers or digital data processing systems for
the latter to process, store, or further transfer
or for transferring data from the computers or digital data processing
systems to the peripheral of information processing system.

This subclass is indented under subclass 219. Subject matter wherein the transceiver or transceiver"s
component is compared by connecting a received path to a transmitted
path and monitoring the output as an indication of the condition
of the transceiver or transceiver"s component.

This subclass is indented under subclass 219. Subject matter including a device that transform a characteristic
of a typical two level pulse or digital data signal into another
form suitable for transmission over a transmission circuit.

(1)Note. An example of a modem is a device which converts
two level pulse signals into two tone signals.

Electrical Computers and Digital Data Processing
Systems: Input/Output,
subclasses 1+ for transferring data from one or more peripherals
to one or more computers or digital data processing systems for
the latter to process, store, or further transfer
or for transferring data from the computers or digital data processing
systems to the peripheral of information processing system.

This subclass is indented under subclass 224. Subject matter including a means for measuring abrupt, spurious
variations in the phase of the frequency modulation of successive
pulses referenced to the phase of a continuous oscillator.

This subclass is indented under the class definition. Subject matter including a delay line tapped at the pulse
or discrete step interval; a set of adjustable attenuators
connected to each tap, except for a main tap, which
attenuators can be used to multiply remaining tap signals by any
number between 1 and minus 1; and a summing network.

(1)Note. Equalizers, per se, if they
include a means to perform mathematical calculations, are
found in Class 708, subclasses 300+ and 819.

(2)Note. Equalizers, per se, are
classified in Class 333. See "SEARCH CLASS" below.
To be classified here, there must be a pulse or digital
communication apparatus.

This subclass is indented under subclass 230. Subject matter in which there is an initial adjustment of
the automatic equalizer prior to use or where a test pulse is sent
through the communication channel to determine what the equalizer
settings should be.

This subclass is indented under subclass 232. Subject matter including either a device which stores a
number and which, on receipt of another number, adds
the two and stores the sum, or a counter with the capability
of counting in an ascending or descending order.

This subclass is indented under the class definition. Subject matter in which the information to be transmitted
is conveyed by means of the relative position of the pulses in a
series of transmitted pulses, the time or spacing between pulses, or
the repetition rate (frequency) of the pulses.

This subclass is indented under subclass 240.03. Subject matter wherein the number of discrete signal amplitudes
is varied according to signal characteristics determined upstream from
the quantization process.

This subclass is indented under subclass 240.03. Subject matter wherein the number of discrete signal amplitudes
is varied according to signal characteristics determined downstream
from the quantization process.

This subclass is indented under subclass 240. Subject matter wherein the pulse or digital signal to be
transmitted is sampled or compared and then converted into a digital
pulse train which represents the amplitude of the sampled signal
at the instant of sampling or comparison, and this digital
pulse train is transmitted so it may be reconverted into a duplicate
of the original signal at a receiver.

This subclass is indented under the class definition. Subject matter in which a signal to be transmitted is sampled
or compared and then converted into a digital pulse train which
represents the amplitude of the sampled signal at the instant of
sampling or comparison, and this digital pulse train is
transmitted so it may be reconverted into a duplicate of the original
signal at a receiver.

This subclass is indented under subclass 244. Subject matter including a means for converting the instantaneous
amplitude of the transmitted signal to the nearest of a fixed number of
discrete amplitude levels, or reverse quantizer.

This subclass is indented under subclass 247. Subject matter where whether a pulse is sent or not is determined
by a criteria other than the amplitude difference of the sampled
and locally decoded waveforms.

This subclass is indented under subclass 247. Subject matter in which the size of the incremental amount
is variable over a wide dynamic range in response to predetermined
patterns in the transmitted series of digital bits or "delta bits" (delta
modulation pulse train).

This subclass is indented under subclass 249. Subject matter where the delta modulation pulse train is
replaced, for transmission purposes, by a derived
pulse train containing fewer pulses, and converting the
derived pulse train back to the delta modulation pulse train at the
receiver.

This subclass is indented under subclass 249. Subject matter in which the companding is instantaneous.

(1)Note. There are two types of syllabic adaptative
modulators namely, the analog syllabic adaptative modulators
and the digital syllabic adaptative modulators depending on whether
the gain control signal of the amplifier is derived from the input
analog input signal or from the coded digital output signal. The
gain control signal may be derived from the input analog signal
using a simple envelope detector. Similarly, the gain
control signal may be derived from the digital output by means of
a syllabic filter. Such syllabic adaptative modulators
will provide a continuous adaptation of the gain of the amplifier
so as to vary the amplitude of the steps of the integrator accordingly. The
instantaneous adaptation or companding is derived from the digital
output signal on a short time basis.

This subclass is indented under subclass 257. Subject matter including an inductive coupling which is
used between the driver and the transmission line or between the
receiver and the transmission line for isolating the d.c. value.

This subclass is indented under the class definition. Subject matter using alternating, sine, or similar
wave currents or using pulsating currents in the transmission and
reception of pulse or digital communications.

This subclass is indented under subclass 259. Subject matter in which more than one transmission channel
is utilized to convey one pulse train.

(1)Note. A channel is a normally independent transmission
path.

(2)Note. Multi-carrier modulation techniques (also
known as orthogonal frequency division multiplexing or discrete multi-tone
modulation) are properly classified here, rather
than in Class 370, unless they are used to transmit multiple sources
of information data.

This subclass is indented under subclass 260. Subject matter in which the transmitted signal can be represented
as the superposition of two modulated signals, each being
obtained by pulse amplitude modulation of a signal sequence on a
sinusoidal carrier, the two signal sequences being generated
in synchronization at the same rate, and the two carriers
being of the same frequency but 90 degrees apart in phase.

This subclass is indented under subclass 261. Subject matter where the binary data rate is above the Nyquist
rate (equal to twice the transmission bandwidth, and
commonly regarded as the upper limit on the rate of binary data
transmission) thereby dispersing the individual input pulses
over more than one signalling interval.

This subclass is indented under subclass 260. Subject matter where the two or more channels carrying the
same message go from the transmitter to the receiver via different
paths, frequencies, or times of transmission.

This subclass is indented under subclass 259. Subject matter in which the pulses are multiplied with a
carrier wave so as to produce and transmit at least one sideband
equal to the carrier plus or minus the baseband.

(1)Note. In amplitude modulation the amplitude of the
carrier wave does not change. The carrier wave can represent the
average amplitude of the envelope and, since this is the
same irrespective of the presence or absence of modulation, the
carrier wave transmits no information. The information
is carried by the sidebands.

This subclass is indented under subclass 268. Subject matter where less than two complete sidebands are
transmitted, with or without the carrier or two complete
sidebands are transmitted without the carrier.

This subclass is indented under subclass 271. Subject matter where the instantaneous frequency of the
pulse or digitally modulated carrier wave is shifted (generally
between two frequencies) according to the presence or absence
of a pulse, or a mark or space, being transmitted.

This subclass is indented under subclass 272. Subject matter wherein the difference between the mark and
space frequencies is at the minimum value still presenting orthogonality (zero cross-correlation) between
the mark and space signals and thus providing for efficient detection
of the data.

(1)Note. Continuous phase is maintained at the mark-space
transitions.

This subclass is indented under subclass 279. Subject matter where the carrier is an elementary alternating
current signal having for each data bit a zero crossing in the same
direction at the beginning of each bit and also at the end of each
bit, a constant duration, a zero crossing only
once intermediate the beginning and the end of each bit, the
intermediate zero crossing representing one of the two signalling
conditions when occurring before the middle of the data bit and
the other of the two signalling conditions when occurring after
the middle of the data bit.

This subclass is indented under subclass 279. Subject matter where there is provision for correction or
reduction of the effects of extraneous pulses or of distortion of
the wave shape of the transmitted signals.

This subclass is indented under subclass 259. Subject matter with provision for correction or reduction
of distortion of the wave shape of the carrier wave or for the correction
or reduction of the effects of extraneous pulses.

This subclass is indented under subclass 286. Subject matter where the binary data rate is above the Nyquist
rate (equal to twice the transmission bandwidth, and
commonly regarded as the upper limit on the rate of binary data
transmission) thereby dispersing the individual input pulses
over more than one signalling interval.

This subclass is indented under subclass 286. Subject matter where the average transmitted amplitude level
for a predetermined group of bits is reduced as far as possible
in attempting to reduce d.c. components.

This subclass is indented under subclass 293. Subject matter having a closed-loop electronic servomechanism
the output of which locks onto and tracks a received clock signal
to provide the frequency and phase aligned receiver clock.

This subclass is indented under subclass 295. Systems where any undesired modulation components accompanying
a desired modulated carrier wave signal, which components
are due to electrical disturbances within the useful frequency band
or any undesired carrier wave distortion and which may originate
at a source external to the transmitter or which may be generated
internally in the transmitter, are reduced, eliminated
or compensated for, or where the transmitted signal may, prior
to transmission, be distorted in a manner complementary
to the distortion introduced in the transmission medium.

This subclass is indented under subclass 295. Subject matter in which the transmitted signal can be represented
as the superposition of two modulated signals, each being
obtained by pulse amplitude modulation of a signal sequence on a
sinusoidal carrier, the two signal sequences being generated
in synchronization at the same rate, and the two carriers
being of the same frequency but 90 degrees apart in phase.

This subclass is indented under subclass 295. Subject matter including two or more transmitters transmit
the same messages through two or more channels via different paths, frequencies or
times of transmission.

This subclass is indented under subclass 295. Subject matter in which the pulses are multiplied with a
carrier wave so as to produce and transmit at least one sideband
equal to the carrier plus or minus the baseband.

(1)Note. In amplitude modulation the amplitude of the
carrier wave does not change. The carrier wave can represent the
average amplitude of the envelope and, since this is the
same irrespective of the presence or absence of modulation, the
carrier wave transmits no information. The information
is carried by the sidebands.

This subclass is indented under subclass 300. Subject matter where less than two complete sidebands are
transmitted, with or without the carrier, or two
complete sidebands are transmitted without the carrier.

This subclass is indented under subclass 303. Subject matter wherein the differences between the mark
and space frequencies is at the minimum value still preserving orthogonality (zero cross-correlations) between
the mark and space signals and thus providing for efficient detection
of the data. Continuous phase is maintained at the mark-space
transitions.

This subclass is indented under subclass 295. Subject matter wherein the output signal of the transmitter
is initiated and terminated by a keying device, such as
a manually or automatically operated switch.

(1)Note. The keying device may control the active elements
of the transmitter (oscillator or modulator) or
the coupling circuits.

(2)Note. Where the claims are drawn to a keying device
controlling an oscillator or an amplifier without additional details
of the transmitter, classification is in Class 331, subclasses
172+ or Class 330, respectively.

This subclass is indented under subclass 309. Subject matter wherein the keying of the transmitter is
automatically controlled as opposed, for example, to
a manual control.

(1)Note. The automatic keying devices of this subclass
include rotating cylinders, disks, etc., with
cams or conductive segments arranged in a predetermined fashion
for closing contacts in the transmitter circuit and controlling
the transmission of intelligence.

This subclass is indented under subclass 309. Subject matter including an auxiliary electron discharge
tube in the keying circuit, the conduction of which controls
the operation of the transmitter and is responsive to the keying means.

This subclass is indented under subclass 309. Subject matter including means controlled by the keying
operation to absorb the oscillations during spacing periods as when
the transmission of intelligence is by marks and spaces, or to
change the impedance or dimension of the antenna to cause modulation
of the carrier.

This subclass is indented under subclass 316. Subject matter wherein the receiver extracts a modulating
signal from an input AM signal whose amplitude of a carrier varies
over a continuum of values in accordance with the modulating signal.

This subclass is indented under subclass 320. Subject matter in which the receiver is responsive to pulses
which are amplitude modulated onto a carrier wave in such a manner
that less than a full carrier or less than two complete sidebands
are created by the modulation process.

This subclass is indented under subclass 329. Subject matter in which the bit interval representing one
of the two binary levels is formed by a change in the phase of the
received signal relative to the preceding bit interval, and
the bit interval representing the other of the two binary levels
is formed by the absence of a change of phase of the received signal.

This subclass is indented under subclass 316. Subject matter in which the pulse or digital information
is received on a carrier wave which is turned on and off at a rate
much higher than the signal rate.

This subclass is indented under subclass 340. Subject matter where a signal to be demodulated is compared
point to point with an internally generated reference signal which
is constructed in such a way that it is at all times a prediction
of what the signal to be demodulated should be at that time.

This subclass is indented under subclass 316. Subject matter where a receiver frequency response characteristic
is set or adjusted in response to frequency changes in the input
signal or charges in the receiver parameters.

This subclass is indented under subclass 346. Subject matter including two separate receivers receiving
the same signal on two different frequencies or at two different
locations on the same frequency or one receiver receiving the same
signal at different times and combining the two thus received signals
into a more noise free signal.

This subclass is indented under subclass 346. Subject matter wherein the noise is reduced by a frequency
domain or digital sequence filter. The filter may remove
interference or pass only desired signals.

This subclass is indented under subclass 316. Subject matter including an electromagnetically operated
switch or an electromagnet with an armature which reciprocates within
and along the axis of an energized coil.

This subclass is indented under the class definition. Subject matter for synchronizing the operation of the receiving
and transmitting mechanisms.

(1)Note. This subclass may include multiplex techniques
used to control synchronization of the transmitter and receiver; however, when
the information content is multiplexed, classification
is in Class 370.

This subclass is indented under subclass 354. Subject matter that receives the synchronizing information
from the information signal itself rather than requiring the transmission
and ultimate reception and separation of a special synchronizing
signal interleaved with the incoming information signal.

This subclass is indented under subclass 354. Subject matter which uses the transmission and ultimate
reception and separation of a special synchronizing signal interleaved
with the incoming information signal.

This subclass is indented under subclass 365. Subject matter where the unique synchronizing word has the
property of being produced by a definite calculation process while
simultaneously satisfying one or more of the standard tests for
statistical randomness.

This subclass is indented under subclass 371. Subject matter wherein a first in-first out (FIFO) storage
is operated to receive data that is synchronized with a write clock
from the input signal and therefrom synchronized with the read clock
of the FIFO storage.

This subclass is indented under subclass 373. Subject matter including a means for controlling the voltage
which applied to the voltage control oscillator (VCO) as
to change the frequency of the phase lock loop.

This subclass is indented under subclass 373. Subject matter having a closed-loop electronic servomechanism
the output of which locks onto and tracks a received signal to provide
the frequency and phase aligned receiver clock.

This subclass is indented under the class definition. Subject matter not provided for in any of the preceding
subclasses of this class.

E-SUBCLASSES

NOTE—E-subclasses in USPC Class 375/E1.001-E7.281
were created as duplicates of EPO groups in H04B 1/69-1/76
and H04N 7/24-7/68. With the
implementation of CPC, these E-subclasses should
no longer be used. Instead, use CPC groups in
H04B 1/69-1/76 and H04N 7/24-7/68.

The E-subclasses in U.S. Class
375 provide for Spread Spectrum techniques in signal modulation
for transmission and systems for the transmission of digital video signal
using pulse code modulation.

This maingroup provides for subject matter utilizing a data
modulated signal which has its energy spread over a transmitted
bandwidth which is much greater than the bandwidth or rate of information
being sent. This subclass is substantially the same in
scope as ECLA classification H04B1/69.

SYSTEMS FOR THE TRANSMISSION OF TELEVISION SIGNALS USING
PULSE CODE MODULATION:

This main group provides for systems for the transmission
of television signals using pulse code modulation, i.e. transmission
systems wherein the television signal is a digital video signal
or a bit stream carrying visual content; e.g., systems, devices
and methods for video bit stream assembling, disassembling, transport, processing, delivery
or control, for source coding or decoding of digital video
signal, for error protection, detection or correction
of digital video signal, for channel coding or decoding
of digital video signal. This subclass is substantially
the same in scope as ECLA classification H04N7/24.

Any Foreign patents or non-patent literature
from subclasses that have been classified have been transferred directly
to FOR Collections listed below. These collections contain
only foreign patents or non-patent literature.
The parenthetical references in the collection titles refer to the
abolished subclasses from which these collections were derived.

Subject matter wherein the spread spectrum signals
are made up of at least two different spread spectrum techniques
such as (a) simultaneous frequency hopping and
direct sequence modulations, (b) simultaneous time
and fre hopping, or (c) simultaneous time-hop
and direct sequence modulations.

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